Delirium is a sudden change in mental status characterized by confusion. Patients find it difficult to pay attention or to think clearly. Between 10 and 30 percent of patients hospitalized with a medical illness experience delirium, according the American Academy of Family Physicians. Delirium may be related to many conditions, but it is always a medical emergency. Elderly people are most vulnerable to delirium.

Changes in both cognition (the mental faculty of knowing) and consciousness (an alert cognitive state) are characteristic of delirium, which tends to develop rapidly. Symptoms include disorientation, difficulty speaking and problems with memory that wax and wane over the course of the day. Symptoms typically worsen during the evening.

The chief causes of delirium are reactions to drugs (including alcohol) or withdrawal from them, in addition to physical and mental illnesses.  Delirium is usually highly reversible – in most cases, it will gradually disappear once the underlying disorder that triggered it is effectively treated or the medication that caused it has been discontinued. However, left untreated, delirium can progress to coma or even death.

Several tests can help diagnose delirium. These include a neurological examination and testing of cognitive function, motor function and levels of sensation. Blood tests, urinalysis and imaging tests may also be performed.